The synthesis of bone collagen is modulated in vivo to meet the changing need for a collagen matrix during the processes of organogenesis, growth and repair. The fetal rat calvarium in vitro can be used to study factors which regulate collagen synthesis. For example, parathyroid hormone and 1 Alpha, 25 dihydroxy vitamin D decrease while insulin increases collagen synthesis. This grant is part of a collaboration effort to define the molecular mechanisms for the actions of these distinctly different hormones. The basis for modulation of collagen synthesis will be assessed at the translational and transcriptional level to probe the basis for the coordinated synthesis of Alpha 1 and Alpha 2 collagen chain. cDNA probes to chick Alpha and Alpha 2 procollagen mRNA have been obtained to initiate the hybridization studies, and rat cDNA and genomic probes will be developed for subsequent studies. The effect of each hormone on collagen synthesis will be correlated with the levels of procollagen mRNA obtained by cell-free translation and Northern hybridization. If a strong correlation suggests transcriptional control, then hybridization studies to obtain rates of procollagen mRNA entry, transcription and decay will be performed. However, if a correlation is not found, then measurement of mRNA utilization (initiation and elongation) and extent of intracellular degradation will be obtained. The RNA studies will also be performed in the osteosarcoma cell line (17/2). The results will be contrasted with freshly isolated calvaria and calvaria maintained in organ culture. Since these tissues contain osteoblasts with varying degrees of differentiation, an indication how a differentiated cell affects higher rates of collagen synthesis will be obtained. The studies will provide insight into how the collagen gene regulates Alpha 1 and Alpha 2 chain synthesis in a coordinated manner. Finally it will define in detail how parathyroid hormone, 1 Alpha, 25 dihydroxy vitamin D and insulin mediate their effects on collagen synthesis.